Conductive materials are frequently formed over semiconductive materials during fabrication of semiconductor chips. In typical processing, a circular wafer of semiconductive material is processed to have one or more thin conductive layers formed thereover. The conductive layers can comprise, for example, metal (such as, for example, copper, aluminum, titanium, tantalum, iron, silver, gold, etc.) or other conductive materials (such as, for example, conductively doped polysilicon). The conductive materials can be subsequently planarized by, for example, electrochemical-mechanical planarization. In electrochemical-mechanical planarization, the conductive material is exposed to an electrical circuit which causes at least some of the conductive material to be electrochemically removed and the material is simultaneously exposed to polishing conditions. The polishing conditions enhance removal of the conductive material and planarize a surface of any remaining conductive material. The polishing can be accomplished by, for example, abrasively removing the conductive material with a polishing pad and polishing slurry.
A difficulty associated with electrochemical-mechanical planarization processes can occur in attempting to maintain a circuit through a conductive material during a simultaneous electrochemical removal and polishing process. It is typical to utilize some portions of the conductive material for carrying current to other portions during the electrochemical removal. For instance, peripheral edges of the conductive material can be connected to a cathode terminal of a power source, a polishing pad connected to an anode terminal of the power source, and the conductive material utilized to complete a circuit between the anode and cathode terminals. A problem which can occur as portions of the conductive material are removed is that such can break an electrical connection to other portions of the conductive material. The breakage of the electrical connection can slow or stop electrochemical removal of such other portions of the conductive material.
In particularly problematic instances, some portions of conductive material will be entirely removed from around other portions of conductive material to leave such other portions as islands surrounded by electrically insulative materials. Such islands will thus have no electrical connection between the anode and cathode, and will not be subjected to electrochemical removal conditions. Accordingly, the removal of the islands will occur entirely through mechanical polishing and will be slowed relative to removal of conductive materials exposed to both electrochemical removal and mechanical polishing. Accordingly, there will be non-homogeneous removal of conductive materials from over a surface of a wafer.
It would be desirable to develop methods of electrochemical removal that avoided some or all of the above-discussed problems.